<SEC-DOCUMENT>0001170010-18-000010.txt : 20180118
<SEC-HEADER>0001170010-18-000010.hdr.sgml : 20180118
<ACCEPTANCE-DATETIME>20180118162559
ACCESSION NUMBER:		0001170010-18-000010
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20180116
FILED AS OF DATE:		20180118
DATE AS OF CHANGE:		20180118

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			FOLLIARD THOMAS J
		CENTRAL INDEX KEY:			0001223841

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-31420
		FILM NUMBER:		18534238

	MAIL ADDRESS:	
		STREET 1:		4900 COX RD
		CITY:			GELN ALLEN
		STATE:			VA
		ZIP:			23060

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CARMAX INC
		CENTRAL INDEX KEY:			0001170010
		STANDARD INDUSTRIAL CLASSIFICATION:	RETAIL-AUTO DEALERS & GASOLINE STATIONS [5500]
		IRS NUMBER:				541821055
		STATE OF INCORPORATION:			VA
		FISCAL YEAR END:			0228

	BUSINESS ADDRESS:	
		STREET 1:		12800 TUCKAHOE CREEK PARKWAY
		CITY:			RICHMOND
		STATE:			VA
		ZIP:			23238
		BUSINESS PHONE:		(804) 747-0422

	MAIL ADDRESS:	
		STREET 1:		12800 TUCKAHOE CREEK PARKWAY
		CITY:			RICHMOND
		STATE:			VA
		ZIP:			23238
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_151631074553704.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-01-16</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001170010</issuerCik>
        <issuerName>CARMAX INC</issuerName>
        <issuerTradingSymbol>KMX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001223841</rptOwnerCik>
            <rptOwnerName>FOLLIARD THOMAS J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>12800 TUCKAHOE CREEK PARKWAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>RICHMOND</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>23238</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-01-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>8000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>72.40</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>423572</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on July 19, 2017.</footnote>
        <footnote id="F2">The shares with respect to this transaction were sold at prices ranging from $72.10 to $72.83.  Upon request, the Reporting Person will provide the Securities and Exchange Commission staff, the Issuer, or any security holder of the Issuer, full information regarding the number of shares sold at each separate price.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Christine Carter, attorney-in-fact</signatureName>
        <signatureDate>2018-01-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
